EXECUTIVE SUMMARY
INTRODUCTION
The City of Sumner authorized the preparation of the Comprehensive Sewer Plan Amendment in
accordance with WAC 173-240-050 as administered by the State of Washington Department of Ecology.
This plan updates the previous Comprehensive Sewer Plan prepared by Parametrix, Inc. in
November 1989.
Since preparation of the 1989 Comprehensive Sewer Plan, the City of Sumner has experienced major
demographic changes that affect the City’s wastewater collection system, including:
•

Reduction of the total Urban Growth Area (UGA).

•

Increased industrial development along 142nd Avenue East.

•

Amendment to the Comprehensive Land Use Plan.

•

Increase in City growth pattern predicted at 3.5 percent per year.

It is the intent of this document to analyze the City’s collection system and to identify system deficiencies
for existing and future flow conditions. If any deficiencies are identified in the City’s collection system,
improvement and cost recommendations will be developed.
COLLECTION SYSTEM ANALYSIS
The City’s wastewater collection system was analyzed for existing and future capacity. The existing
system’s condition was also assessed. The collection system capacity determines the ability to
hydraulically convey the wastewater flows to the treatment plant. The system’s condition and reliability is
determined by examining the age of the system and deficiencies identified by City personnel. Using this
information and the analysis components below, Parametrix was able to determine if any system
deficiencies exist:
•

Comparison of the current collection system capacity to a simulated current peak day flow.

•

Review of the existing system’s condition and identification of potential impacts on the overall
system’s reliability.

•

Comparison of existing system capacity to a simulated future peak day flow for the existing
service area.

•

Expansion of the collection system into unserved areas of the UGA boundary (future service
area).

Existing Peak Day Flow Simulation (Existing Service Area)
The capacity of the existing collection system was compared to a simulated peak day wastewater flow
generated for the City’s current service area. Both the existing pipeline capacity and the simulated peak
day flow were calculated using a computer program called “HYDRA.” HYDRA calculates the capacity of
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the City’s existing pipelines and pump stations using conventional engineering formulas and assumptions.
A detailed description of HYDRA and its operation is provided in Chapter 5.
An existing peak day flow simulation was calculated based upon land use and the percentage of build-out
of properties within the city’s service area, plus the anticipated contribution of infiltration and inflow (I/I)
of stormwater entering the City’s sanitary sewer pipelines during winter months. I/I assumptions were
calculated separately for each pump station basin and manually entered into the computer program. I/I
was calculated between 500 and 2,000 gallons per acre per day (gpad) depending upon the age of the
pipelines within individual pump station basins and the amount of I/I indicated by pump station run times
recorded during wet weather conditions.
The percent build-out of properties within the City’s service area was established using visual observation
of aerial photos of the Sumner valley. Once the flow simulation was completed, it was compared to
existing treatment plant records to validate results of the computer model. Based upon the result of the
computer modeling, the simulated peak day flow for the Sumner service area was calculated at 3.1 million
gallons per day, which compared reasonably well to actual peak day flows of 2.7 million gallons per day
recorded at the Sumner treatment plant.
Future Peak Day Flow Simulation (Existing Service Area)
The future peak day flow simulation was generated using the computer model HYDRA. This flow
simulation used the same methodology as the existing peak day flow simulation, with the following
exceptions:
•

It was assumed that all of the area currently served by the City’s existing wastewater collection
system would be at 100 percent build-out. Based upon the rate of growth within the City of
Sumner, it was estimated that build-out of the service area would occur between 20 and 25 years.

•

It was assumed that the City would reduce I/I in the pump station basins with older pipeline not to
exceed 500 gpad.

The future peak day flow simulation was compared to the capacity of the existing City pipelines and
pump stations to determine if capacity deficiencies could occur as the existing service area builds out.
Expansion of the Collection System to Accommodate the Entire UGA
Portions of the City’s UGA are not yet served by the City’s existing wastewater collection system. Those
areas are shown on figures within this report and are described as follows:
•

The area bounded by the Stuck River on the west, Lake Tapps on the east, Elm Street on the
south, and the Pierce County line on the north.

•

The region bounded by SR 167 on the east, the City of Edgewood on the west, 16th Street East on
the north, and Caldwell Road East on the south.

•

The region located along Valley Avenue East west of SR 167 near the existing city cemetery.

•

The region located along 160th Avenue East south of SR 410.

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Adding service area to the City’s wastewater system will increase the total wastewater flow to the
wastewater collection system downstream of the connection point. Impacts to the City’s existing
collection system from additional service areas were determined by simulated future wastewater flows
using the entire UGA acreage. Flow simulation for the entire UGA was generated by adding those
unserved portions of the UGA to the future peak day flow simulation previously discussed. The only
exceptions to the assumptions within the future peak day flow simulation included:
•

The increased service area size to accommodate the additional UGA acreage.

•

The area east of East Valley Highway was assumed at 40 percent of total land utilization due to
steep topography.

System Reliability
The condition of the existing system was examined to determine if there are potential impacts to the
reliability of the collection system. The system’s condition was established by interviewing City of
Sumner maintenance staff, reviewing the results of the modeling exercise, and researching the age of the
collection system pipelines and pump stations throughout the City’s system. Those portions of the City’s
collection system that need to be upgraded over the next 20- to 25- year planning period were noted and
improvements were recommended.
SYSTEM CAPACITY IMPROVEMENTS
Listed below are improvements recommended to correct the capacity deficiencies in the existing
collection system resulting from existing peak day flow volumes:
•

Increase the existing capacity of the Parker Pump Station from 285 gpm to 950 gpm. Ultimately,
the Parker Pump Station will need to be upgraded to 1,800 gpm to accommodate future peak day
flows. Replace the existing 6-inch-diameter force main with 4,000 feet of 10-inch force main
from the Parker Pump Station to a new discharge at Wood Avenue.

•

Increase the existing capacity of the Van Tassel Pump Station from 135 gpm to 365 gpm. Extend
the 4-inch-diameter force main from the current discharge approximately 1,800 feet further west
along Elm Street to a new discharge at Wright Avenue.

•

Increase the existing capacity of the 16th Street Pump Station from 700 gpm to 1,400 gpm.

•

Replace approximately 1,400 lf of existing 10-inch gravity pipe main with 12-inch pipe from the
16th Street Pump Station east along 16th Street, then south along Wright Avenue to between
Langdon and Washington Streets.

•

Increase the existing capacity of the Tacoma Street Pump Station from 175 gpm to 372 gpm.

Following are improvements recommended to correct capacity deficiencies in the existing collection
system resulting from future peak day flow volumes:
•

Increase the capacity of the Cherry Street Pump Station from 534 gpm to 1,180 gpm.

•

Increase the capacity of the South Street Pump Station from 1,115 gpm to 1,750.

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Following are improvements recommended to provide capacity to the collection system to allow for
expansion into unserved portions of the service area (UGA boundary):
•

Increase the capacity of the 142nd Street Pump Station from 2,300 gpm to 5,200 gpm. Install a
new 14-inch force main parallel to the existing line from the existing station to a new discharge at
the intersection of W. Main Avenue and Fryar Avenue. This improvement is contingent on the
actual industrial wastewater flow meeting or exceeding per acre flow estimates.

•

Expand the capacity of the 16th Street Pump Station No. 2 from 100 gpm to 160 gpm.

COLLECTION SYSTEM UPGRADES
The following improvements are recommended to upgrade the collection system, reduce I/I, extend the
lifecycle of the collection system, and extend the life and capacity of the treatment plant.
•

Collection System Upgrades
Pipe Main Rehabilitation/Replacement Program

$8,100,000

Hydraulic Intertie Removal

$54,800

Infiltration and Inflow (I/I) Program

$150,000

Flow Meter Installation at each Station

$190,500

On-site Generator Installation

$307,200

Electrical System Upgrades

$23,800
Subtotal:

$8,826,300

TOTAL PROJECTED COST IN 1999 DOLLARS:

$14,680,900

WASTEWATER TREATMENT PLANT CAPACITY IMPACTS
Based upon all indications, the City of Sumner’s treatment plant has sufficient capacity to accommodate
growth within the collection system given the following assumptions:
•

WWTP expansion is completed by 2003.

•

Average collection system growth rates do not exceed 3.5 percent.

•

The City continues aggressive identification and reduction of existing system infiltration and
inflow (I/I) to a system-wide average of 500 gpad.

•

The City encourages the use of alternative collection systems where appropriate.

•

The City coordinates I/I reduction efforts with the City of Bonney Lake and unincorporated
Pierce County.

FUTURE SOUTHERN SERVICE AREA
It is understood that the City of Sumner wishes to extend sewer service to the region south of the existing
UGA boundary. The City has depicted expansion of the service area in three previous documents.
Table ES-2 lists the previous City of Sumner documents and the approximate area of the proposed
expansions.
The feasibility of extending service to this region was evaluated to determine what policies, regulations,
and laws were in place that could govern expansion of the wastewater collection system. Under the
Growth Management Act, the City is prohibited from direct annexation and providing utility service to
any area outside of its existing UGA boundary.
The City may apply for an inter-agency agreement with Pierce County Regional Council called a “Joint
Planning Area.” The agreement allows the City and County to jointly establish design, land use, building,
capital facilities, and environmental criteria for the region.

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The potential impact to the wastewater treatment plant capacity was reviewed based upon expansion of
the collection system into the future southern service area. It was determined that providing sewer service
beyond the existing UGA boundary will require additional treatment plant capacity. Table ES-2
summarizes the magnitude of additional capacity needed to serve the three possible expansion regions.

Average wastewater flow was assumed to be 1,300 gpad with I/I flows of 500 gpad and a peak factor of 2.2.
Joint Planning Area

(b)

FINANCING PLAN
A financing plan was prepared to provide an indication of the impacts on the City’s existing sewer fees to
finance the recommended improvements for the collection system outlined in this report and the
wastewater treatment plant improvements listed in the Wastewater Treatment Facility Final
Comprehensive Plan Amendment No. 1 as prepared by Gray & Osborne. The plan focused upon funding
1. capacity improvements by generating revenues from the System Development Charges, and
2. system upgrades by generating revenues from the sewer utility rates.
The two separate funding options considered as part of this plan are:
•

Funding Option 1 Assumptions:
¾ Capacity improvements will be paid by revenues generated from system development charge
(SDC).
¾ Upgrades to the system will be paid through sewer utility rates.
Option 1 also assumes that the City’s existing debt payment will continue to be paid by revenues
generated by sewer utility rates, and revenues from the golf course and land lease.

•

Funding Option 2 Assumptions:
¾ Capacity improvements will be paid by revenues generated from SDC.
¾ Upgrades to the system will be paid through sewer utility rates.
Option 2 assumes that half of the existing annual debt payment will be paid by revenues
generated by SDCs and that the remainder of the debt will be paid by revenues from the golf
course and land lease.

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Projected impacts upon the SDCs and the sewer utility rates by the two funding options is summarized in
Table ES-3.

It is recommended the City consider Funding Option No. 2 that includes a combined SDC and sewer
utility rate increase along with payment of approximately half of the City’s existing debt payment through
revenues generated by SDCs. This option is more equitable to existing and future system customers for
the following reasons:
•

Growth pays for growth – The future system customers pay for the capacity improvements
necessary to provide them service.

•

Existing users pay for system upgrade – The customers who have been using the system would be
responsible to pay for the system upgrades that benefit all customers.

To finalize the financial element of the sanitary collection system and treatment plant planning, it is
recommended that the City of Sumner conduct a detailed financial analysis prior to implementing rate
adjustments. A detailed financial analysis will confirm or deny the impacts of the recommended system
improvements on the existing sewer fees.

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1.
1.1

INTRODUCTION

BACKGROUND

The City of Sumner authorized preparation of a Sanitary Sewer Comprehensive Plan Amendment in
accordance with the Department of Ecology regulatory requirements. The previous revision to the City’s
Sanitary Sewer Comprehensive Plan was prepared by Parametrix, Inc. in November of 1989. Since
preparation of the 1989 Sanitary Sewer Comprehensive Plan, the City of Sumner has experienced changes
to the city’s demographics that would affect the wastewater collection system. Major changes to the
City’s demographics over the last 10 years include:
•

Establishment of an Urban Growth Area (UGA) that is smaller than the 1989 Sanitary Sewer
Comprehensive Plan service area.

•

Development of the Industrial Area along 142nd Avenue East between the Stuck River and
northern boundary of Pierce County.

•

Update of the zoning map in October 1997.

•

Amendment of the Comprehensive Land Use Plan, October 1997.

•

Anticipated and actual population increases averaging 3.5 percent per year.

1.2

PLANNING GOALS

It is the City’s goal to ensure that the 2000 amendment to the Sumner Sanitary Sewer Comprehensive
Plan includes the following:
•

Demographic changes that affect the sanitary sewer collection system.

•

Evaluation of the condition and capacity of the existing wastewater collection system.

•

Establishment of wastewater collection system improvements necessary to upgrade the existing
collection system.

•

Establishment of improvements to the City’s existing wastewater collection system to provide
adequate capacity to serve future City wastewater users.

•

Recommendations of the wastewater collection system improvements necessary to extend the
wastewater collection system into portions of the UGA that are not currently being served.

•

Estimates of the probable capital costs for improvements to the City’s existing wastewater
conveyance system to meet existing and future needs.

•

Estimates of the impact to the City’s sanitary sewer rates necessary to fund recommended
improvements.

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1.3

PLAN REQUIREMENTS

The Plan has been prepared in accordance with the requirements of the Department of Ecology and the
Washington Administrative Code. Chapters 2 and 3 of this document fulfill the information requirements
of WAC 173-240-050. This Plan update also integrates previous wastewater plans, including:
•

Sewer Collection System Comprehensive Plan, City of Sumner, Parametrix Inc., November 1989;

•

Feasibility Study for Sewer Service to North End of Sumner, City of Sumner, Parametric, Inc.,
December 1987.

Existing conditions and service area demographics affect the wastewater collection system, including
physical features such as the size of the service area, land use and zoning population variations, soils,
groundwater conditions, and topography. Climate and economic factors also play an important role in
planning community utility systems. Collectively, the factors discussed in this chapter and Chapters 3
and 4 have a considerable impact on the processes involved in determining the location, size, and extent
of the sanitary sewer collection system facilities, and the ability of the community to accept the financial
burden of improvements. These factors are briefly described in this chapter.
2.2

BOUNDARY AND SERVICE AREA

The City of Sumner is located approximately 11 miles southeast of the City of Tacoma. The City of
Sumner corporate limits is generally found northeast of the convergence of the Puyallup and Stuck Rivers
(see Figure 2.1). Land within this area is subject to the City’s municipal code, ordinances, resolutions, and
policies. Other agencies with limited jurisdiction include the Sumner School District, Sumner Fire
Department, Fire District No. 22, Pierce County Health Department, and all State and Federal agencies.
The City of Sumner sanitary sewer service area is the City’s Urban Growth Area (UGA) (see Figure 2.1).
A portion of the UGA is not served by the City’s wastewater collection system. The 6.83-square-mile
(4,336 ac) area designated as the Urban Growth Area contains over 179,000 lineal feet (33.90 miles) of
sewer mains. The City and Pierce County coordinated activities in developing an annexation policy and in
identifying the Urban Growth Boundary in accordance with countywide planning policies. The Sumner
UGA boundaries coincide with Sumner city limits.
In accordance with the State Growth Management Act (GMA), the boundary of the Urban Growth Area
established in 1997 was based upon the following:
•

20-year population forecast

•

Environmental constraints

•

Concentration of existing development

•

Existing infrastructure and services

•

Location of existing and proposed transportation corridors

•

Areas the City could extend and provide urban services to logically and economically

It is expected that within the 20-year time frame of the Comprehensive Land Use Plan that sewer, water,
stormwater, utilities, telecommunications, and transportation may be extended to developments in all or
most of the areas outlined in the UGA.

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2.3

HISTORY

The City of Sumner was first platted in 1883 and incorporated in 1891. The City of Sumner began a
collection system in 1927. The initial system combined sanitary sewer and stormwater collection. This
system discharged through seven outfalls, four along the Stuck River and three along the Puyallup River.
Of the seven original outfalls (overflows), only two remain today. Each of the remaining outfalls have
each been equipped with manually operated control valves.
The first wastewater treatment plant, pump stations, and sanitary sewer force main system were installed
in 1957. Additional pump stations have been installed at various times during the expansion of the
system. The North Pump Station remains the oldest station in the system. It was initially installed in 1957
and it was upgraded in 1986. The following table lists the Cityâ&#x20AC;&#x2122;s pump stations, year of construction, last
year rebuilt or refurbished (if known), and station capacity.

Table 2-1. Pump Station Characteristics
Pump Station
Tacoma

Year Constructed

Last Year Rebuilt

1982
1987

Type

Station Design
Capacity (gpm)

Dry/Wet Well

175

North

1957

Dry/Wet Well

300

Van Tassel

1977

Submersible

135

Jansen

1979

Submersible

130

Parker

1963

Dry/Wet Well

285

th

16 Street

1967

Dry/Wet Well

700

Cherry

1966

Dry/Wet Well

535

South

1966

Dry/Wet Well

1,500

1996

Submersible

130

1998

Submersible

100

th

160 Street
th

16 PS No. 1
th

16 PS No. 2

1998

Submersible

100

142nd Street

1998

Submersible

2,280

Figure 2.2 shows the locations of the City of Sumnerâ&#x20AC;&#x2122;s existing pump station and manually controlled
emergency overflows.
2.4

LOCATION, TOPOGRAPHY, AND SOILS

The regional topography has been developed by the natural drainage of the Stuck and Puyallup Rivers and
major mudflows from Mount Rainier over the millennia. Due to these influences, the majority of the City
of Sumner has a flat terrain with steep hills to the east and west.
Elevations in the valley range from 40 feet above mean sea level to 90 feet, based upon the 1929 National
Geodetic Vertical Datum (NGVD) for the City of Sumner. Ground slopes typically range from 0 to 5
percent. The highest point within the city limits is approximately 680 feet above mean sea level near the
eastern end of the city near Lake Tapps. Hillside slopes along both east and west of Sumner range from
20 to 70 percent. Figure 2.3 shows the planning area topography.
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According to the U.S. soil Conservation Service, the general soil type in the Sumner valley area is
classified as alluvial sediment. This type of soil is considered poor load bearing soil and highly
susceptible to earthquake liquefaction due to the extremely high groundwater table in the valley areas.
The soil types identified on the eastern hillside region are “Kapowsin” and “Alderwood,” gravelly loams
generally found on till plains. These classifications are composed of several primary soils, each with
various characteristics and limitations. The soil type identified along the base of the eastern and western
hillsides is classified as “Xerochrept,” a till soil with high strength, which allows the areas to form steep
cliffs.
Groundwater observation wells in the Sumner valley have shown that the groundwater levels range from
8 to 11 feet below the surface during dry-weather periods and 2 to 8 feet below the surface during wetweather periods. Historically, excavations in the Sumner valley require trench dewatering and foundation
support to properly construct deep to moderately deep underground gravity sanitary sewer and pump
station improvements.
2.5

CLIMATE

Climate and weather are critical factors in wastewater system planning, design, and engineering. With
respect to wastewater system planning, the amount of precipitation impacts the amount of infiltration and
inflow within a system. Infiltration and inflow is defined as surface and/or groundwater that enters the
sanitary sewer collection system and contributes to the total wastewater volume.
Summers in Sumner are mild and warm (average daytime temperature in the mid 70s) and winters are
comparatively mild (average daytime temperature in the 40s). Precipitation is usually in the form of rain,
with occasional snow in the winter. The City of Sumner averages 42 inches of precipitation annually with
monthly variations from a low of 0.95 inches in August to a high of 6.65 inches in November. The
prevailing wind is southerly to southwesterly most of the year. The following table indicates average
precipitation and temperature for each month.

Table 2-2. City of Sumner Average Temperature and Precipitation
Month

Average Temperature (°F)

Average Precipitation (inches)

January

42.4

5.51

February

45.6

4.35

March

47.7

4.20

April

52.4

3.97

May

57.5

2.39

June

63.5

1.96

July

70.6

1.18

August

68.8

0.95

September

62.7

1.45

October

51.4

3.10

November

46.7

6.65

December

40.5

5.91

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2.6

INDUSTRY

The City of Sumner has a number of industries such as Sonoco, Golden State Foods, and Western Wood
Preserving that are located north of Elm Street. The City has also recently seen a rapid increase in the
construction of warehouse-type facilities and businesses in the light industrial zoned area along 142nd
Avenue East between the Stuck River and the northern Pierce County line. A copy of the current
industrial user survey for the City of Sumner’s collection system is included in Appendix A of this report.
The City of Sumner is served by both Union Pacific and Burlington Northern railway lines; however, the
area is currently oriented toward automobile/truck access.
2.7

WATER SUPPLY

The City of Sumner owns and operates the water system for the city limits and the area of Pierce County
south of the Puyallup River to approximately 96th Street East. Water supply is provided from four
separate springs located within the City’s watershed and two artesian wells. The spring sources are
Sumner, Weber No 1, Weber No. 2, and County springs. The City’s well sources are Cemetery and
South. The protected watershed is located along the eastern edge of the city limits. Cemetery well is
located near the southwestern edge of the city limits and South well is located beyond the current city
limits south of State Route 410.
There are a number of private wells within the region. The exact number and location of private wells
have not been defined.

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3.
3.1

POPULATION PROJECTION AND LAND USE DESIGNATIONS

INTRODUCTION

Population and land use information contains within this chapter is the basis for projecting wastewater
volumes and sizing the collection system facilities discussed in Chapter 4. Wastewater volumes were
projected using two independent methods:
•

Service Area Population Method: Calculating the total service area wastewater flow based upon
the number of residents within the Sumner urban growth area (UGA).

•

Land Use Method: Calculating the total service-area wastewater flow based upon the type of land
use and the percent build-out of land within the Sumner UGA.

The Service Area Population Method is a common tool for determining wastewater flow from a city or
service area.
The Land Use Method is also a common method for determining the volume of wastewater generated
within a portion of the service area or basin. By adding all individual basin flows together, the total flow
from the City can be determined.
The Land Use Method was used to estimate wastewater flow and size the collection system facilities. The
Service Population Method was used to verify the results of the hydraulic modeling program.
3.2

POPULATION

Since incorporation in 1891, the residential population of Sumner increased from 1,200 residents at the
turn of the century to 8,900 residents in 1999, as shown in Table 3-1. The average annual growth rate has
been approximately 3.2 percent since 1990. The City’s Planning Department estimates a continued
average annual growth rate of 3.5 percent over the next 25 years.

Table 3-1. City Population
Year

City Population

Population Change per
Decade
–

Average Annual Population
Change (%)

1950

2,816

–

1960

3,155

339

1.1

1970

4,325

1,170

3.2

1980

4,936

611

1.3

1990

6,459

1,523

2.7

1999

8,900

2,441

3.2

Table 3-2 is the population estimates for the City of Sumner through the year 2025 based upon data
provided by the City of Sumner Planning Department.
Table 3-2. City Population Projection
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Year

City Population

Population Change

Average Annual Population
Change (%)

2000

9,211

331

3.5

2005

10,570

1,359

3.5

2010

12,554

1,983

3.5

2015

14,910

2,366

3.5

2020

17,708

2,798

3.5

2025

21,031

3,323

3.5

3.3

LAND USE, ZONING, AND SERVICE AREA

The City of Sumner established the Sumner UGA in 1997 in cooperation with Pierce County and
surrounding communities. The Land Use Section (Section Q) of the Sumner Comprehensive Plan Update
was developed in accordance with the Growth Management Act to address land use within the City. The
Land Use Section has also been developed in conformance with countywide planning policies.
Existing land use includes residential, commercial, and industrial development, as shown in zoning and
land use figures provided by the City of Sumner (see Figures 3.1 and 3.2). Table 3-3 summarizes the
current zoning classifications.

High Density Residential – 20 units per acre includes apartment, condos, and townhouses

GC

General Commercial

NC

Neighborhood Commercial

CDB

Central Business District

M1

Light Manufacturing

M2

Heavy Manufacturing

AG

Agriculture includes forest lands and mining

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Wastewater flows generated in areas of the UGA that lie outside of the current zoning map were
calculated using the land use designations taken from the City of Sumner Comprehensive Land Use Plan
listed in Table 3-4. These areas include the following portions of the UGA:
•

Along 166th Avenue East south of SR 410.

•

The area bounded by East Valley Highway on the west, 166th Avenue East on the east, the City of
Sumner watershed on the south, and 16th Avenue East on the north.

•

The area bounded by 8th Street East on the south, the Pierce County line on the north, the Stuck
River on the west, and East Valley Highway on the east.

•

The area bounded by 148th Avenue East on the east, 137th Avenue East on the west, 16th Street
East on the south, and 8th Street East on the north.

•

The area bounded by Sumner-Tapps Highway on the west, 171st Avenue East on the east, 64th
Street on the south, and 55th Street on the north.

Table 3-4. Land Use Classification
Abbreviation

Description

LDR1

Average of LDR12 and LDR 8.5 – 3.28 units per acre

LDR2

Average of LDR7.2 and LDR6 – 5.50 units per acre

The land use designation of the area owned by the City of Sumner bounded by the Stuck River on the
west, East Valley highway on the east, 8th Street East on the north, and 40th Street East on the south was
categorized as public land-use designation rather than the current agricultural zoning classification.

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4.
4.1

WASTEWATER FLOW PROJECTIONS

INTRODUCTION

Chapter 4 develops flow projections that are used to size individual capital facilities within the
wastewater collection system. To project wastewater flow volumes, it was necessary to establish the
following:
•

Identify the existing peak day flow generated in the City of Sumner’s service area.

•

Estimate the components of the existing peak day flow, including residential/commercial and
industrial wastewater flow, and system infiltration and inflow (I/I).

•

Simulate the existing peak day wastewater flow conditions using the Land Use Method, and
compare these wastewater flow projections to existing flow data at the wastewater treatment
plant.

•

Land Use Method – Wastewater flow projections were prepared by multiplying a given
wastewater flow per acre (based upon land use) by the size of a basin. Wastewater flows using the
Land Use Method are generated as a product of the system hydraulic analysis conducted in
Chapter 5. The hydraulic analysis computes wastewater flow projections for the entire service
area and for individual basins contained within the service area. The Land Use Method of
wastewater flow projection was used to size the City of Sumner’s collection system facilities.

•

Determine the existing per capita peak day wastewater flow originating from
residential/commercial users. The per capita peak day wastewater flow is used to validate
projected future wastewater flows simulated by the Service Area Population Method.

•

Service Area Population Method – Wastewater flow projections for the entire service area were
established by multiplying the number of people in the service area by an estimated peak day
wastewater volume per capita. The number of people within a service area is directly proportional
to the volume of wastewater discharged into the wastewater collection system and ultimately to
the wastewater treatment plant.

•

Systems that have a large percentage of commercial and industrial land use must also be
considered independently from the service area population since employed personnel most likely
live outside of the community but contribute to the community’s wastewater flow during the
business day. The City of Sumner has experienced recent industrial and business development
along 142nd Avenue between the Stuck River and the northerly Pierce County line. Development
of this commercial and industrial land will affect the total wastewater volumes generated within
the service area.

Future wastewater flow projections calculated using the Population Method were compared to projections
using the Land Use Method to validate the system hydraulic analysis.

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4.2

EXISTING PEAK DAY WASTEWATER FLOW

The City of Sumner’s wastewater treatment plant operational reports were investigated to determine the
existing peak day flow. The peak day wastewater flow was then used to verify the land use flow
projection calculated by the hydraulic modeling program.
On January 2, 1997, the Sumner wastewater collection system experienced a peak day flow of 2.70 mgd
(see Operational Report, Appendix B).
4.2.1

Peak Day Wastewater Components

The components of the existing peak day flow were estimated using the City of Sumner’s I/I reports,
water usage records, and industrial survey information. The components were estimated in order to
calculate an existing service area wastewater flow for the City of Sumner’s collection system
(Section 4.5). The existing peak day flow is comprised of residential/commercial and industrial
wastewater flows along with system infiltration and inflow.
The peak day I/I and industrial flow component information is summarized below:
•

The industrial flow component is 0.15 mgd, based upon the City of Sumner’s water records and
industrial survey (Appendix D).

Using the above information, an existing peak day wastewater flow volume was determined using the
following formula:
(Peak Day Residential/Commercial Wastewater Flow) = (2.7 mgd) – (1.6 mgd) – (0.15 mgd)
Peak day residential/commercial wastewater flow was then estimated to be 0.95 mgd. The per capita peak
day flow has been calculated in Section 4.5 using this information.
4.3

LAND USE METHOD

Chapter 3 established the land-use components used to project wastewater flow in the City of Sumner
wastewater collection system. The following steps were used to project total collection system flow:
•

Separate the City of Sumner’s wastewater collection system into smaller service areas defined by
the City’s existing pump station basins.

•

Estimate the volume of wastewater flow from each of the land-use components.

•

Estimate the volume of I/I flowing into the system from each of the pump station basins.

•

Analyze the City’s collection system using a computer program specifically written to produce a
hydraulic model for a wastewater collection system based on land use. Parametrix selected
“HYDRA” for the modeling program. Details of the computer model are contained in Chapter 5.

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4.3.1

Collection System Basins

The total collection system was subdivided into basins in order to assess the existing and future capacities
of the collection system facilities within the individual basins. Parametrix selected the land area that can
be served by an existing pump station as a basin.
The boundaries for the area flowing into each pump station were identified using the City of Sumnerâ&#x20AC;&#x2122;s
facilities map shown in figure 4.1. Using AutoCAD, the total area contained within each of these basin
boundaries was determined. Table 4-1 summarizes each of the Cityâ&#x20AC;&#x2122;s pump station boundary areas.

Table 4-1. Pump Station Boundary Areas
Basin

Area (ac)

Tacoma

44.7

North

126.7

Van Tassel

94.5

Jansen

14.3

16th

266.2

WWTP

173.0

Cherry

283.9

South

199.6

Parker

258.1

nd

142

791.0

th

16 PS-1

18.2

16th PS-2

67.4

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4.3.2

Land Use Wastewater Flow Estimates

While Chapter 3 provided the method to establish the flow volume projection, this chapter will estimate
the actual volume of peak day wastewater produced for each of the land uses on a per acre basis.
Table 4-2 summarizes the flow per acre from each of the land-use designations.

Table 4-2. Wastewater Flow Estimates Based Upon Land Use
Land Use(a)

Flow (gpad)

LDR12

625

LDR1

750

LDR8.5

880

LDR7.2

1,050

LDR2

1,150

LDR6

1,250

MDR

2,300

HDR

4,600

GC

1,500

NC

1,500

CBD

1,500

M1

1,300

M2

1,300

AG

250

UV
(a)

Variable

For land-use abbreviations, see Tables 3.3 and 3.4.

Peak day wastewater produced from residential land-use classifications were calculated using the
following assumptions and equation:
•

The contribution of I/I was assumed to be a separate component of the wastewater flow.
For comparison purposes, the Department of Ecology’s Criteria for Sewage Design standards are 100
gpcd with a minimum of 3 people per unit. These design standards include normal infiltration and inflow.
The 1989 Sewer Collection system comprehensive Plan established design standards of 100 gpcd and 2.5
people per unit.
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For the complete calculation of land-use flows, please refer to the spreadsheet in Appendix A of this
report.
4.4

STORMWATER INFILTRATION AND INFLOW ESTIMATES

The I/I estimates are based upon the City of Sumner’s annual I/I report. The City of Sumner assumes the
difference between wet- and dry-weather pump station run time constitutes the total storm-induced I/I for
the collection system. Collection system I/I estimates were used, along with pump station basin areas, to
determine a per acre I/I distribution for each of the pump station basins.
The City of Sumner’s wastewater collection system conveys stormwater in the form of I/I to the
wastewater treatment plant during wet-weather conditions.
Stormwater infiltration is groundwater that seeps into the wastewater collection system through pipe
cracks, faulty joints, and faulty manholes. The quantity of water that may infiltrate into a sewer system is
rather indeterminate and will generally increase with the age of the sewer system.
Stormwater inflow consists of water that may enter the wastewater collection system through illegal
connections such as roof gutters, area drains, catch basins, and unplugged clean-out openings.
4.4.1

Total Infiltration and Inflow

The total infiltration and inflow for the City of Sumner’s collection system was estimated by comparing
the wet- and dry-weather pump station run times taken from the City’s I/I report.
The wet- and dry-weather pump station run times for the years 1996, 1997, and 1998 were compiled into
a spreadsheet (see Appendix B). The difference between the wet- and dry-weather flows for the sum of all
the pump stations was assumed to be the total peak I/I.
This analysis assumes that the total peak day I/I is the difference between wet and dry weather, but
infiltration may exist during the summer due to the high localized groundwater table and the age of the
existing system. Summertime infiltration would have to be identified in a detailed I/I study outside the
scope of this report.
As outlined in Appendix B, the total peak I/I for the City of Sumner’s collection system was calculated at
approximately 1.6 mgd.
4.4.2

Infiltration and Inflow Distribution

A spreadsheet was prepared (see Appendix B) comparing the pump station run times for wet and dry
weather to determine an appropriate distribution of I/I throughout the City of Sumner’s individual pump
station basins as summarized below:
•

The difference between the high wet-weather and low dry-weather flows was assumed to be the
I/I contribution from that pump station basin.

•

The sum totals of I/I from the individual pump station basins were assumed to be the total
collection system I/I.

•

Percent of I/I contribution from each station was determined by dividing I/I flow per each basin
by a total I/I flow of all basins.

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â&#x20AC;˘

Three years of data was combined to determine an average value of I/I (mgd) for each pump
station basin.

Table 4-3 is a summary of the I/I percentage and total I/I from each pump station per day. For a more
complete calculation, see Appendix B of this report.

Table 4-3. Wastewater Pump Station Infiltration and Inflow Estimate
Station

Average I/I as a Percent of Total
Basin I/I (%)

I/I (mgd)

Tacoma

2.0

0.03

North

3.0

0.05

Van Tassel

4.0

0.06

Jansen

1.0

0.02

16th and WWTP

37.0

0.60

Cherry

10.0

0.16

South

16.0

0.26

Parker

27.0

0.43

Total I/I in City System (mgd):

100%

1.61 mgd

Infiltration and inflow records were not available at the time of preparation of this plan amendment for
160th Street, 16th Street PS No. 1, 16th Street PS No. 2, and 142nd Street Pump Stations previously listed in
Table 2-1. The pump stations listed are new, and the City does not have sufficient records on winter and
summer flows to be able to conclude a significant impact from I/I. The City does not appear to experience
noticeable I/I in these systems. Apparently, the collection pipelines connected to these pump stations are
just beginning to serve customers in the 142nd Street industrial area. It is anticipated that as more sanitary
sewer users access the system and gravity collection systems are extended to industrial properties that I/I
will increase to these pump stations. An I/I value of 500 gpad was assumed for any properties not
currently being served by the Cityâ&#x20AC;&#x2122;s wastewater collection system.

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Using the information from Tables 4-1 and 4-3, a distribution of I/I on a per acre per day basis was
determined for each of the collection system basins. Table 4.4 summarizes this distribution.

Table 4-4. I/I Distribution
Basin

Area (ac)

Tacoma
North
Van Tassel
Jansen

I/I (mgd)

I/I (gpad)

44.76

0.071

1,600

126.72

0.070

550

94.52

0.053

600

14.27

0.012

800

16th and WWTP(a)

439.17

0.829

1,900

Cherry

283.90

0.132

500

South

199.62

0.090

500

Parker

258.15

0.516

2,000

(a)

4.5

Due to the lack of pump station data for the WWTP basin, the basin area was combined with the 16th Street basin to
determine an I/I distribution.

SERVICE AREA POPULATION METHOD

The service area population wastewater flow was calculated to verify the future wastewater flow
projected through the Land Use Method by the hydraulic modeling program. To project total population
flows for the City of Sumner, a current population flow was established according to the following
formula:
•

The current peak day wastewater flow based on population is 104 gpcd, representing residential and
commercial projected flow.
4.6

TOTAL PROJECTED WASTEWATER FLOW

The existing peak day estimated wastewater flow in the service area was calculated using a computer
program that features hydraulic modeling capabilities. The computer program used by Parametrix, Inc. to
perform the hydraulic modeling is “HYDRA,” which uses the Land Use Method to determine total peak
day wastewater flow generated throughout the service area. Specific details of the HYDRA program are
contained within Chapter 5.
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The HYDRA model calculates the theoretical peak-day flow and the peak instantaneous flow expressed in
gallons per minute. The result of the HYDRA model is then compared to actual historical wet-weather
wastewater flow at the Sumner treatment plant to verify that the engineering assumptions included within
the model are reasonable. If the results of the HYDRA model are substantially different than actual
wastewater flows at the treatment plant, the land-use-wastewater flow assumptions entered into the model
have to be modified.
Parametrix, Inc. also compared the results of the HYDRA model to the wastewater flow projections
calculated using the Population Method as discussed earlier. Comparison of the wastewater flows also
assumed that build-out of the service area would be equal to the population increase experienced by the
City over the next 25-year planning period. The results of the flow projections are included in Table 4-5.

Table 4-5. Wastewater Flow Projections (peak day)
Source

Average Annual Growth
Rate (%)

Current Peak Service Flow
(mgd)

HYDRA Flow Simulations

Land Use

3.1

5.5 (build-out)(a)

WWTP Base Flow (b)

3.5

2.7

6.4 (year 2025)

(b)

3.0

2.7

5.7 (year 2025)

3.5

2.7

5.3 (year 2025)

WWTP Base Flow
(c)

Population
(a)

(b)

(c)

Projected Peak Flow (mgd)

Using existing peak day flow and projecting flow increases to match the projected population increase of 3.5 percent per
year, the collection system will reach build-out peak day flow in 23 years. Assumes correction of excessive I/I to
approximately 500 gpad.
Assumes existing WWTP peak day flow projected forward by growth rate listed. Assumes that the current rate of I/I is
not reduced.
Population projected flow was determined using a projected population of 21,033 (year 2025), a total service area of
4,336 acres, and an industrial flow of .964 mgd. The industrial flow volume for this calculation was taken from the
hydraulic model.

Upon review of the differing flow projections, it appears that the wastewater flow assumptions based on
land use are reasonable.

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5.
5.1

SYSTEM EVALUATION

INTRODUCTION

The condition and capacity of the City’s existing collection system facilities is evaluated in this chapter.
This evaluation has been separated into the following sections:
•

Identified System Deficiencies: Identify deficiencies in the existing collection system not
attributed to a capacity deficiency.

•

Hydraulic Capacity: Calculate the hydraulic capacity of the existing collection system and
compare the conveyance capacity to existing and future wastewater flow conditions.

•

Collection System Extension: Address extension of the City’s wastewater collection system into
portions of the UGA that are not currently being served.

•

Recommended System Improvements: Recommend improvements to the existing collection
system that will correct existing deficiencies and provide sufficient capacity for service to
existing and future wastewater customers.

5.2

IDENTIFIED SYSTEM DEFICIENCIES

Existing collection system deficiencies are indicators of inadequate capacity, overloaded pipe segments,
or needed system repairs. During an interview with City personnel, known system deficiencies were
identified in the existing collection system facilities, including:
•

Interviews were conducted with City personnel to identify deficiencies within the collection system
pipeline. A map was prepared showing deficiency locations and severity. Also included were areas that
required ongoing periodic maintenance, such as jetting or areas that experienced surcharging during wet
weather. Figure 5.1 shows these identified areas. Table 5-1 lists the approximate locations and collection
pipeline deficiencies as reported by City personnel.

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Table 5-1. System Collection Pipeline Deficiencies
Street

Cross Street Locations

Deficiency

Chestnut

McKinnon and Cherry

Pipeline Wet Weather Surcharge

Alder

Willow and Thompson

Pipeline Wet Weather Surcharge

Valley

Main

Pipeline Wet Weather Surcharge

Fryar

North of Bridge Street

Belly in pipeline, grease accumulation

Main

East of Ryan

Solids disposition, jetting

Sumner

North and Washington

Solids disposition, jetting 1/week

Mead-McCumber

East of Parker

Solids disposition, jetting 1/month

nd

Mead-McCumber

East of 152 Avenue

Solids disposition, blockage

Washington

West of Valley

Solids disposition, jetting 1/quarter

Elm

E. Valley Highway

Shattered pipes

Silver

East of Sumner

I/I, roots

5.2.2

Identified Pump Station Problems

It is the City personnel’s opinion that the pump stations considered to be problems are Parker, North,
Tacoma, and 16th Street. The following problems were identified by City personnel during the interview
process:
•

16th Street Pump Station wet well overflows after a 10 minute power outage.

•

Hydrogen sulfide (H2S) corrosion problems at the Tacoma Pump Station.

•

Capacity is inadequate at the Parker Pump Station.

•

Grease accumulation occurs in the wet well at the North Pump Station.

•

Capacity is inadequate at the Van Tassel Pump Station.

5.2.3

Identified System Improvements

City personnel also identified additional improvements for the wastewater collection system to improve
system reliability. The following items are the improvements identified by personnel during the interview
process:
•

Install either level or flow meters in the existing pump stations to increase the City’s ability to
monitor the system better (currently only 142nd Street, 16th Street PS-1, and 16th Street PS-2 have
both capabilities).

•

Improve system wiring and standardize where possible at all pump stations. This will also allow
for development of a spare parts inventory.

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•

Update and standardize older motor starters and electrical controls.

•

Redesign Jansen Pump Station control panel and piping to provide a quick disconnect for existing
motor removal.

•

Install isolation valves to isolate flow entering all stations.

•

Install valves between Parker and Van Tassel gravity mains to control surcharging.

•

Improve site access to South and Cherry Pump Stations.

5.2.4

Pump Station Basin Intertie

Parametrix and City personnel have also identified a hydraulic intertie in the system (see Figure 5.2). A
system of gravity overflow pipe segments link the Parker, Van Tassel, and 160th Pump Stations
hydraulically.
During peak wet-weather flows, these overflow pipes allow excess flow in the Parker Pump Station basin
to enter the Van Tassel basin. Excess flows from the Van Tassel basin then enter the 160th Street Pump
Station basin, which then pumps wastewater back to the Parker basin through a 4-inch force main. During
peak wet-weather flows, wastewater is pumped in a circle causing excessive pump run times and an
assumption that these pump stations are actually experiencing a higher volume of I/I than may actually
exist.
5.3

HYDRAULIC CAPACITY

The hydraulic capacity of the existing wastewater collection system was analyzed using the computer
software program “HYDRA.” HYDRA simulated existing and future wastewater flows based upon
engineering assumptions entered into the computer program. By comparing the existing collection system
capacity with simulated existing and future flows, capacity deficiencies in the collection system can be
identified.
HYDRA was developed by Pizer, Inc. of Washington. It is a flexible program developed for analysis of
storm and wastewater systems. Its menu-driven format allows AutoCAD and GIS integration, and the
command files are user-friendly. Flow criteria and development scenarios can be developed in several
ways, and each pipe segment can be analyzed for gravity or pressure flow conditions. Pump stations may
be modeled for one-, two-, or three-pump scenarios. For this analysis, firm pumping capacity was
assumed at each station. Firm pumping capacity assumes the largest pump at each station is out of
service. For example, on a duplex system it was assumed only one pump was operating.
The pump station basis areas were divided into smaller sub-basins, and link data from the City’s existing
facilities maps was compiled. A “link” is the upstream manhole and the reach, or length, of pipe
downstream to the next manhole. The link data includes length, ground elevation upstream and
downstream, invert elevations upstream and downstream, pipe diameter, and pipe material.

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The system data is entered through command and design parameter menus according to the requirements
of the HYDRA program. HYDRA utilizes various commands for sanitary sewer analysis and modeling.
Existing and proposed pipe criteria must be defined. Among these criteria are:
•

Pipe roughness parameters

•

Flow depth to pipe diameter (d/D)

•

Minimum pipe slope

•

Minimal flow velocity

•

Flow injection method

HYDRA uses two different methods to “inject” flows into the system. These flows can be calculated by
either population (per capita) or by land use (zoning).
In the population flow method, the number of people living within a region of the sewer system is entered
along with an average flow per person per day (generally 80-100 gallons/day). HYDRA then compares
the per capita data with the “link” date to determine the amount of flow through each pipe.
In the land-use flow method, each of the City’s zoning codes is assigned a flow per acre value. These
flows are based on the average number of houses that could be built within an acre of land, the average
number of people per house, and the average flow per person. HYDRA then compares the land-use data
with the links data to determine the amount of flow through each pipe. As previously discussed in
Chapter 4, the method selected by Parametrix for this analysis was the Land Use – Sewer Service Basin
Intersection Method.
The intersection of the established land use with the delineated sub-basin is then considered by HYDRA
to be the flow from that sub-basin. HYDRA uses an established or input diurnal curve to “inject” the flow
into the system. These flows are injected at select points, called nodes, within the sewer system and
HYDRA calculates travel time to the link. The process then repeats until the total flow of the system
reaches the “outfall” point. The last pipe segment into the treatment plant was chosen as the outfall point
for this analysis.
The HYDRA model for the City of Sumner does not evaluate every segment of a wastewater collection
system but models all of the main trunks of the system. Main trunks are considered pipe segments 8
inches in diameter or greater connected to individual collection lines serving less than 20 acres, and
collection pipeline that could be extended to serve portion of the UGA that are not being services. These
segments were generally located along the northern and eastern edges of the City’s existing system.
5.3.1

Existing Collection System, Existing Wastewater Flows

The initial hydraulic analysis of the City of Sumner wastewater collection system identified system
deficiencies that are attributed to capacity. The hydraulic analysis assumed existing wastewater flow
conditions simulated by the HYDRA computer program. Existing flows were simulated by estimating the
current percent of land build-out for each portion of the service area.

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Parametrix established the percent of build-out within each of the land-use areas through visual inspection
of City of Sumner aerial photographs that were prepared by Nies Mapping Group in the summer of 1999.
The hydraulic analysis of the current wet-weather flow conditions identified surcharging in the following
basins and pipe segments (see Figure 5.3):
•

Parker Pump Station surcharged the following segments due to inadequate station capacity:
¾ North along Parker Road from Main to Garden Street.
¾ The first pipe segment south of the pump station at Main and Parker Road.
¾ The segments at the intersection of 63rd Street East and Parker Road.
¾ The pipe segment from Parker Road east along 63rd Street East.
¾ The segments west along Main Street between Parker Road and Graham Street.
¾ The segments from Parker Pump Station east along Main to 160th Avenue East, then south to
64th Avenue East, then east to the end of the analysis.

•

16th Street Pump Station surcharged the following segments:
¾ From the pump station both north and south along Bonney Avenue due to inadequate pump
station capacity.
¾ East along 16th Street East to Wright Avenue, then south through the high school, then east to
Valley, then south to 63rd Street Court East due to contribution from the Parker Pump Station.
¾ East along Wright Avenue to Valley, then north to Elm, then east to the end of the analysis
due to the existing pipe capacity and contribution from the Van Tassel Pump Station.

The hydraulic analysis also identified the following pump stations with existing capacity less than
existing peak day wet-weather wastewater flows.
•

HYDRA was also instrumental in analyzing pipeline segments identified by City personnel as
potential problems. The following areas of concern are described earlier in this chapter
(Section 5.2.1):
¾ HYDRA did not indicate any surcharging of the pipe segments along Alder north of Willow
as reported by City personnel. It is likely that surcharging is being caused by an obstruction in
the pipe.
¾ HYDRA indicates a reverse slope situation in the pipe segment along 158th Avenue and
Mead-McCumber. The available City data/map may be incorrect and verification may be
necessary. The segments downstream of this site have been described as needing jetting
monthly, which may indicate that a reverse slope condition does exits.
¾ HYDRA did not indicate any surcharging along Chestnut between McKinnon and Cherry at
existing flow conditions. It is likely that the reported line surcharging is being caused by an
obstruction in the pipe.
¾ City personnel indicated the pipe segment along Washington requires frequent jetting and
shows signs of surcharging. HYDRA indicated surcharged all along these segments due to
undersized pipe segments downstream from the Sumner Presbyterian Church north to Wright
Avenue, then west along 16th Street to the pump station. Routine surcharging of the
downstream pipe segments could result in solids deposition in the Washington pipe segments.

5.3.2

Existing Collection System, Future Wastewater Flows

The second phase of the hydraulic analysis identified deficiencies in the existing collection system
assuming future build-out of the service area (UGA).
When analyzing service area for future build-out conditions, the I/I allowance for 16th Street, the
Wastewater Treatment Plant, and Tacoma and Parker Pump Station basins were all assumed to be 500
gpad. This assumption is based upon the premise that these basins will undergo I/I investigation,
maintenance, and repairs to correct the existing system deficiencies, thereby lowering each basin’s
estimated I/I per acre.
Pump stations with insufficient capacity for future wastewater flows are:
Existing Capacity (cfs)

The 10-inch pipe segments east along 16th Street beginning at the 16th Street Pump Station to
Wright Avenue, then south along Wright Avenue to between Langdon and Washington Streets.

The areas identified by City personnel with deficiencies or routine maintenance problems were again
reexamined with the following conclusions:
•

HYDRA did not indicate any surcharging of the pipe segments along Alder north of Willow even
under future build-out flow conditions indicating an obstruction may exist in the pipeline.

•

HYDRA did not indicate any problems along Chestnut between McKinnon and Cherry at future
build-out flow conditions indicating an obstruction may exist in the pipeline.

•

The surcharging in the 10-inch pipe segment along Washington Street, near Wright Avenue,
increased with the increasing flows as expected due to the undersized pipe segments downstream.

5.3.3

Future Collection System Extensions, Future Wastewater Flows

A product of the hydraulic analysis included the configuration and sizing of future collection system
improvements necessary to serve portions of the UGA not currently connected to the City of Sumner
wastewater system. Existing system capacity information generated in Sections 5.3.1 and 5.3.2 was used
to decide where collection system extensions could occur with the least amount of impact to downstream
collection system facilities. As shown on Figures 5.4 and 5.5, extensions of the City’s collection system
are recommended where existing collection pipelines have sufficient hydraulic capacity to accommodate
wastewater flows generated by build-out of the UGA. Once the collection system configurations were
established as shown on Figures 5.4 and 5.5, the HYDRA computer program was used to size the various
gravity pipelines based upon the wastewater flow volumes anticipating build-out of the individual basins.
Through this iterative process, the following was determined:
•

The region west of SR 167 near the City’s cemetery (Cemetery Basin) should be connected to the
existing collection system across Bridge Street.

•

The area at the southeastern edge of the City’s service area (Parker Basin), south of SR 410,
should be connected to the existing system directly to the Parker Pump Station.

•

The area east of Sumner-Tapps Highway between 64th Street East on the south and 55th Street
East on the north (Parker Basin) should connect to the existing system directly to the Parker
Pump Station.

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•

The area (Tacoma Basin) bounded by Elm Street on the south, Salmon Creek on the north, the
Burlington North Railway line on the west, and the City’s watershed on the east should connect
to the existing system through the Tacoma Pump Station basin.

•

The area bounded by the Stuck River on the west, Salmon Creek on the south, the City’s UGA
boundary on the east, and the Pierce County line on the north should connect to the existing
system through the 142nd Street Pump Station basin.

There were two alternatives proposed to serve the basin(s) east of the Stuck River. These alternatives are
fully described below.
5.3.3.1

Alternative 1 – Collection System Extension

Providing sewer service to the UGA through the Alternative 1 configuration would involve the
installation of two major pump stations (see Figure 5.4). Preliminary design estimates place the location
of these pump stations at 41st Street East and 8th Street East.
Service throughout the region would be established using a combination of gravity and alternative
collection methods in combination with the two above-mentioned pump stations.
The 8th Street East Pump Station would service the area both north and south of 8th Street. Flows to the
pump station would be through conventional gravity sewers to the pump station. Wastewater would then
be pumped south along East Valley Highway through a 10-inch force main to 24th Street East. Additional
flows between the pump station and 24th Street East would be collected into the 10-inch force main
through use of alternative collection technology.
At the intersection of 24th Street East and East Valley Highway, collected flows from the area north of
Forest Canyon Road along with the area approximately ½ mile south of this intersection would combine
with the force main using alternative collection technology.
The wastewater flows would then continue through a 12-inch force main west across the Stuck River
using the existing pedestrian bridge and into the 24-inch gravity sewer located along 142nd Avenue East.
The 41st Street East basin would include the remaining area south of Forest Canyon Road to the existing
sewer system basins. Flows along the eastern hilltop region would be collected through a series of gravity
sewers to a major trunk line directed to the East Valley Highway. Any flows collected north of this point
along East Valley Highway should be collected through alternative collection technologies. The
combined wastewater would then flow south to 41st Street East through gravity trunk lines.
Flow from the wastewater collection system south of 41st Street East but north of Salmon Creek would be
collected through gravity sewers. The two flows would combine at the intersection of 41st Street East and
East Valley Highway and continue west to the second pump station.
All collected wastewater would then be pumped through a 12-inch force main across the Stuck River and
into the 24-inch gravity main located along 142nd Street East.

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5.3.3.2

Alternative 2 – Collection System Extension

Alternative 2 required the same number of major pump stations as in Alternative 1 (see Figure 5.5). The
primary difference is routing the 8th Street East Pump Station force main south by southeast into the 142nd
Street basin at 16th Avenue East.
The flows collected along East Valley Highway would again be collected through alternative collection
technology, but under this scenario the required force main is 6 inches minimum rather than 10 inches as
shown in Alternative 1. The wastewater would continue south to the intersection of East Valley Highway
and 24th Street East.
The flows from north of Forest Canyon road and the small area south of the Forest Canyon Road and East
Valley Highway intersection would again combine and flow west along 24th Street East. Again there is a
reduction in the required force main from a 10-inch minimum to an 8-inch minimum.
There would be no changes to the design criteria of the 41st Street East Pump Station basin.
Either of these alternatives assume that all flow from the areas shown must be routed through the 142nd
Street Pump Station. Routing any additional significant flow from the UGA into the existing system,
other than 142nd Street Pump Station, created pipeline and pump station surcharging and overloading in
the system. Either alternative will work, and final system configuration has been left to the City.
5.3.3.3

Alternative Collection System Technology

Alternative forms of wastewater collection are recommended for portions of the City of Sumner service
area. As previously identified in Chapter 5 and as shown on Figures 5.4 and 5.5, isolated portions of the
City’s service area have been identified as being served by conventional gravity collection or alternative
forms of wastewater collection. Both options have been identified to allow the City of Sumner the option
of considering either technology at the time of design and/or ULID formation. By listing both options, the
Department of Ecology (DOE) will accept either technology. If alternative forms of wastewater collection
are not listed or conversely conventional gravity is not listed, then DOE will require that the City use the
collection technology listed within the planning document.
Using the following criteria, alternative forms of wastewater collection are proposed for isolated portions
of the City of Sumner.
•

Cost-effective in areas with limited wastewater flow or in areas zoned for low-density
development.

•

Extends the life of the City’s wastewater treatment plant. Alternative forms of wastewater
collection have substantially less wet-weather flow than conventional gravity because of limited
I/I influence. Some forms of alternative collection can even have lower organic load being
discharged to the City’s wastewater treatment plant since pretreatment occurs at the individual
buildings.

•

Results in lower ULID cost than a gravity alternative. Alternative sanitary sewer collection lines
represent approximately 20 to 40 percent of the cost of an alternative form of collection system.
The remainder of the capital costs related with alternative collection is associated with the
installation of the portion of the utility that is installed on private property.

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As previously denoted in Figures 5.4 and 5.5, only certain portions of the City’s collection system were
identified for the use of either conventional gravity or alternative collection. Those portions of the service
areas identified were selected based upon:
•

areas zoned for low density housing or land use that typically has lower wastewater generated on
a per-acre basis,

•

areas with difficult construction challenges. Construction challenges specific to the City of
Sumner include:
¾ The presence of high groundwater that substantially increases the cost of deep sewer line
installation due to dewatering and trench safety costs.
¾ Soils that have limited foundation characteristics which could result in pipe settlement over
time, affecting the liquid-carrying capability of the pipeline.
¾ Road reconstruction and traffic control challenges resulting from conventional gravity sewer
installation due to the depth and width of the sewer line trench.
¾ Construction equipment and sewer material stockpiling.
¾ Areas that present difficult permitting requirements such as installing sewer lines under a
water body or wetland. Alternative forms of wastewater collection are typically under
positive pressure and can readily be installed using trenchless technology under sensitive
areas, which eliminates some of the permitting requirements associated with conventional
sewer line construction.

Available Alternative collection Systems
There are four primary alternative collection systems that are employed throughout Washington State
when conventional gravity conveyance is not cost effective and/or viable. These alternative forms of
wastewater collection and conveyance are defined in the Department of Ecology manual titled Criteria
for Sewage Works Design, prepared in December 1998. The four primary means of conveyance include:
•

Septic Tank Effluent Pump System (STEP)

•

Small Diameter Gravity System (SDG)

•

Grinder Pump System

•

Vacuum Collection System

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Septic Tank Effluent Pump System (STEP)
A STEP system works somewhat like a conventional septic tank. A vessel, or STEP tank, is installed at
each structure and provides pretreatment as it separates the solids from the liquid stream of conventional
raw sewage. The liquid portion of the wastewater stream is then conveyed by a pump system to a small
diameter pipeline in the public right-of-way and into a municipalityâ&#x20AC;&#x2122;s wastewater treatment facility.
Because the majority of the solid matter has been removed from the wastewater, very small diameter
pipelines can be utilized, as small as 2-inch diameter or larger, depending on the hydraulic capacity
needed. Since most of the solids have been removed, minimum scouring velocities in the pipelines are not
required. Other alternative forms of collection and conventional gravity pump stations and force mains
require a minimum pipeline velocity of 2 ft/sec to eliminate plugging. A STEP system also includes the
advantage of offering pretreatment within each STEP tank. The organic load from a STEP tank includes a
reduction of suspended solids of approximately 85 percent and a reduction of BOD5. or biochemical
demand of approximately 30 percent.
Small Diameter Gravity System (SDG)
A SDG system is essentially the same as a STEP system with one exception. Those homes that are
substantially higher than the pressure gradient in the pressure pipeline do not require installation of a
pump to convey wastewater to the municipalityâ&#x20AC;&#x2122;s treatment facility. Each tank above the hydraulic grade
line is commonly equipped with a filter to ensure that solids do not enter into a small diameter pipeline.
Since SDG uses a tank for pretreatment, minimum scouring velocities, required in other alternative
systems, are not necessary. It is common practice to combine SDG tanks and STEP tanks on common
pipelines.
Grinder Pump System
A grinder system utilizes pipeline sizes that are similar to a STEP, typically a 2-inch minimum diameter
and larger depending on the hydraulic capacity needed. Primarily, the difference between a grinder
system and STEP/SDG is that the entire raw solid and liquid wastewater components are macerated
through the grinder pump and then conveyed through small gravity pipelines to the treatment facility.
Since the system grinder conveys all solids introduced to the wastewater system, a minimum scouring
velocity of 2 ft/sec must be maintained in the pipelines to ensure that plugging of the pipeline does not
occur.
Vacuum Collection System
A vacuum system differs substantially from STEP, SDG, and grinder pump systems. The previously
described technologies use positive pressure to convey wastewater from individual users to the
wastewater treatment plant. A vacuum system uses a negative pressure or a vacuum to pull the
wastewater to a centralized pump station. After the wastewater arrives at the pump station, it is then
conveyed to the treatment plant using a conventional positive pressure pump. Vacuum lines are similar to
other alternative systems in constructability as vacuum lines use a minimum 4-inch-diameter line size that
can be constructed in a narrow trench at depths typically ranging from 4 to 7 feet. Vacuum systems also
employ a solenoid pit at each multiple structure. The vacuum pit is the mechanical device that receives
the sewage and then allows the sewage to be conveyed by pipeline to a centralized vacuum pump station.

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Alternative System Evaluation
Based upon review of the characteristics of the City of Sumner’s service area, the following
recommendations for selection of an alternative technology should gravity not be viable for certain uses
are within the service areas.
•

A combination of STEP and SDG should be considered in areas where gravity is not viable. It is
assumed that the City owns the small diameter collection mains within public right-of-way and
that individual homeowners are responsible for ownership and operation of STEP tanks on
private property. This recommendation was based upon the following criteria:
¾ STEP/SDG can be designed for 24 hours of emergency storage in the event of a power outage
or need of mechanical repair. Even though power outages are infrequent within the Sumner
Valley, the storage volume allows property owners time to make repairs to their systems
should individual mechanical parts need maintenance.
¾ STEP/SDG has electrical components that are applicable for residential or commercial
applications.
¾ STEP/SDG reduces both wet weather wastewater flow volumes and organic load to the
wastewater treatment plant. This advantage allows the City to increase the number of users
within the service area without exceeding the allocated plant capacity for the Sumner service
area.
¾ STEP/SDG does not require a minimum scouring velocity within the pipelines. Lack of
scouring velocity allows the City to connect users to the sewer pipeline as the need arises
without concern of pipe plugging. Other alternatives require a minimum number of users be
connected to the pipeline to assure that the minimum scouring velocity of 2 ft/sec is
maintained.

•

A grinder system could be used for certain portions of the collection system if the following
requirements are achieved by the manufacturer:
¾ Application to the Washington State Department of Labor and Industries Electrical Division.
¾ 24-hour minimum storage requirements as stated in the “Criteria for Sewage Works Design”
prepared by the Washington State Department of Ecology.

•

A vacuum system has an initial higher cost than other forms of alternative collection. Based upon
“a rule of thumb” provided by the manufacturer, a minimum of 350 equivalent dwelling units are
required before vacuum is cost comparable to other collection alternatives. Most, if not all, of the
isolated areas shown for alternative sewers will generate a sufficient number of customers to
make a vacuum system cost affective.

There are disadvantages to alternative forms of wastewater collection and specific disadvantages to the
recommended alternative of STEP/SDG systems. The City needs to be aware of the following
disadvantages when considering use of alternative collection systems.
•

Responsibility for ownership and operation of the individual pump unit is placed on the property
owner. This is a responsibility that is not common to a conventional gravity collection system and
is an additional burden to the property owner. That burden, however, is offset by the lower ULID
cost associated with construction of the pipeline within the public right-of-way.

•

The City has a responsibility to assure that the STEP/SDG tanks are watertight and free of
infiltration and inflow. An inspection program will need to be established that guarantees
privately installed tanks and pumps meet City requirements. To assure that I/I is not introduced
into the STEP/SDG system over time, the City may also need to conduct a periodic review of the
STEP/SDG tank.

•

The wastewater originating from a STEP/SDG system is septic. Discharge to a gravity collection
line can result in odors and corrosion caused by the release of hydrogen sulfide. Odor control and
corrosion control must be addressed when considering this alternative.

5.3.4

Policies Associated with Alternative Collection Systems

All wastewater systems require the municipality to adopt certain policies regarding ownership and
maintenance responsibilities. Alternative collection systems being different than conventional gravity
systems require special consideration from the City staff, elected officials, and the sewer users. Key issues
that should be considered include:
•

Will the City allow alternative forms of wastewater collection to be considered within the service
area?

•

If the City considers alternative forms of wastewater collection (i.e., STEP/SDG), will the City or
the property owner be responsible for ownership, operation, and maintenance of the onsite
pumping unit?

•

If the City allows alternative sewers to be used, will the sewer user be able to select between
alternative collections on conventional gravity?

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6.
6.1

WASTEWATER SYSTEM IMPROVEMENTS

INTRODUCTION

Chapter 6 presents the recommended wastewater collection system improvements that address identified
existing system deficiencies resulting from poor system conditions or lack of adequate system hydraulic
capacity. These recommendations provide a planning guide to establish future capital improvement plans,
preparation of city budgets, and implementation scheduling.
6.2

System improvements shown on Figures 5.4 and 5.5 that are necessary to expand the City’s wastewater
collection system into unserved areas of the UGA are not discussed in this chapter. It is assumed that
these improvements will be constructed as part of a developer extension or formation of a ULID.
6.2.1

Existing System Capacity Improvements

Improvements to the existing collection system facilities include system expansion to provide adequate
capacity to serve existing and future wastewater customers. These improvements include:
•

Parker Pump Station/Basin Improvements:
¾ Expansion of Parker Pump Station from a 285 gpm (0.635 cfs) station to a 1,800 gpm (4.0
cfs) facility. Expand and extend the force main from Parker. The existing 6-inch force main
should be replaces with a 10-inch force main and extended from its present terminus at
Valley Avenue west along Main then north to Wood Avenue.
¾ Increase the size of the gravity inlet pipe to Parker Pump Station to 21 inches minimum.
¾ Direct additional expansion in the agricultural area south of Mead-McCumber to Valley
Avenue.

System improvements requested by the City of Sumner public works staff or recommended by
Parametrix, Inc. include
•

Parametrix Recommended System Upgrades:
¾ Parker/Van Tassel/160th Streets Hydraulic Intertie:
Eliminate the hydraulic intertie for the Parker, Van Tassel, and 160th Street Pump Stations.
This improvement must be completed after the previously discussed upgrade of the Parker
Pump Station and force main.

•

Sanitary Sewer Main Rehabilitation/Replacement Program:
Currently, the City of Sumner has approximately 179,000 lineal feet of existing sanitary sewer
main. Using information from the Whitacre and Associates 1956 Study and Preliminary Plans for

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Sewerage and Sewage Treatment Plant Facilities. This report contained a General City Map
showing the existing and proposed City of Sumner collection system.
Parametrix established that 81,029 lineal feet of the City’s collection system existed or was
constructed in 1956. This means 45 percent of the existing system will be at, or beyond, the
normal 50-year useful life expectancy of the installed collection pipes on or before the year 2006.
If the City of Sumner were to initiate a 45 percent main rehabilitation/replacement program over
the next 50 years, it would require the rehabilitation or replacement of 1,620 lineal feet each year.
For main replacement, the average cost per lineal foot for an 8-inch main is approximately $300.
Different rehabilitation methods can be broken into costs per lineal foot. Following is a summary
of the different possible methods and an estimate of the associated costs:
¾ Cast-in-Place (CIP) Pipe Lining

$75.00/lf

¾ Fold and form Pipe Lining

$55.00/lf

¾ Link Pipe Stainless Steel Sleeve

$1,500 for 12 inches to $2,000 for 36 inches

¾ CIP Spot Repair

$1,500 for 3 feet to $2,000 for 30 feet

¾ Line Grouting
– Sealing
– Side Sewer Grouting

$15-$20 per joint
$300 per side sewer

Using an average cost per lineal foot for rehabilitation, or repair of $200 per lineal foot, the yearly
cost for this program would be approximately $324,000, which may be fiscally difficult for the
City to achieve.
•

Infiltration and Inflow Program:
Throughout the system analysis and as a result of interview with City staff, the presence of
stormwater infiltration and inflow will have an increasing importance on the City’s system. We
therefore make the following additional recommendations:
¾ Increase the I/I testing program throughout the City. Conduct wet-weather/dry-weather flows
analysis to determine in which basins to concentrate initial I/I reduction efforts.
¾ Expand close-circuit video inspection and smoke testing beginning within the oldest sections
of the City.

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•

City of Sumner System Upgrades:
The following is a list of improvements requested by City personnel that are appropriate for this
general sewer plan. The list includes only the requested improvements that have not been
addressed in prior sections of the chapter. Improvements include:
¾ Install flow meters on all pump stations.
¾ Install on-site generators at South, North, Tacoma, and Cherry pump stations.
¾ Schedule replacement of older motor starters and electrical controls. Standardize installations
to develop a spare parts inventory.
¾ Upgrade electrical services at Cherry and 16th Street Pump Stations to include a neutral
conductor. Currently these stations are wired for delta ground, which creates hazards for City
personnel. Parker Pump Station was also identified with this wiring problem, but was not
included because it has been recommended for replacement.
¾ Refurbish Jansen Pump Station with quick disconnect pumps and motors.

6.3

PRIORITIZATION OF RECOMMENDED IMPROVEMENTS

Recommended Collection System Improvements were prioritized to assure that the most critical projects
are completed first. The highest priority projects are improvements to existing pump stations and
pipelines that eliminate hydraulic surcharging caused by existing wet-weather peak day flows. The next
level of priorities are:
•

Ongoing identification and elimination of excessive sources of I/I.

•

Improvements to system reliability identified by the City of Sumner staff.

•

Pump station and pipeline improvements that eliminate surcharging caused by future wet-weather
peak day flow.

•

Elimination of hydraulic surcharging caused by existing wet-weather peak day flows:
¾ Parker Road Pump Station and force main expansion or replacement.
¾ Van Tassel Pump Station and force main expansion or replacement.
¾ Tacoma Pump Station expansion or replacement.
¾ Increase 10-inch gravity pipe segments to 12-inch segments east along 16th, then south along
Wright Avenue to south of Langdon.
¾ 16th Street Pump Station expansion.

Expansion of the 142nd Street Pump Station:
¾ The existing 880-acre industrial area has been expanded to approximately 3,280 acres.
¾ It has been assumed that industrial zoned areas will contribute an average peak flow of
1,300 gallons per acre day to the 142nd Street Pump Station. Actual peak day flows could be
difficult depending on the actual buildings constructed.
¾ It is recommended that the City of Sumner delay any planned expansions for this pump
station until a more complete record of the actual industrial wastewater flows have been
recorded.

6.4

CAPITAL IMPROVEMENT PROGRAM

The Capital Improvement Program shown on Table 8-1 has been developed to clarify the cost and priority
of each of the improvements previously listed. The 1999 project cost for each improvement is shown,
along with the projected period of construction. The project costs have been adjusted based upon a
3.5 percent inflation rate.
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8.4

PROCESS FOR EXTENSION OF SERVICE AREA

8.4.1

Growth Management Act

In 1990, the State legislature adopted the Growth Management Act (GMA), which limited the ability of a
municipality to provide utility service to areas outside of an established urban growth boundary.
The GMA was adopted to increase coordination among state and local governments, improve data
sharing, and resolve conflicts. Its intent was to curb land-hopping development and to prevent the loss of
natural resources.
The Revised Code of Washington (RCW) 35.13.005 states:
“No city or town located in a county in which urban growth areas have been designated under
RCW 36.70A.110 may annex territory beyond an urban growth area.”
Therefore, any annexation plans for the region south of the current UGA boundary cannot take place until
the boundary is extended to include the southern region. The City may be able to influence growth
(zoning) and building standards in the region until extension of the UGA occurs.
8.4.2

Joint Planning Areas

Due to the limitations imposed by the GMA, the City should go through Pierce County Regional
Council’s Joint Planning Areas to address concerns about future sewer service. Instituted in 1993, the
Joint Planning Area policy was created to facilitate and accomplish joint planning in areas of mutual
concern.
The framework for the establishment of a Joint Planning Area has been set forth in Pierce County
Resolution 93-127 (see Appendix E). Through this process, the City of Sumner will be able to establish
the following criteria for the region:
•

Determination of exact boundaries for the joint planning area.

•

Current and future land use designations.

•

Environmental standards and policies.

•

Development and design standards.

•

Delineation of growth tiers and connection with transition plans for level of service standards and
provision of service.

•

Development of a transition plan allowing for capital facilities and utilities planning.

•

Identification, discussion, and resolution of mutual concern, including annexation issues.

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Pierce County Planning stated that establishment of Joint Planning Areas is currently the subject of a
newly formed subcommittee. As the City to seeks resolution of the ultimate southern UGA limits, it
becomes a joint effort by the City Council and the County. The location of the final UGA and service area
limits affects all subsequent decisions and collection system design.
To avoid this region becoming difficult to serve with sanitary sewer at some point in the future, it is
recommended that the City of Sumner proactively seeks to establish both zoning and construction criteria
through collaboration with Pierce County Regional Council and County agencies. To accomplish this, the
City must formally begin the process of requesting a Joint Planning Area assignment for this region.
8.4.3

Establishment of Joint Planning Area

The process for establishing a Joint Planning Area requires an interlocal agreement between the City of
Sumner and Pierce County. The interlocal agreement must include the following information:
•

The duties and responsibilities for the signatory agencies.

•

A process for outside review of the agreement.

•

The agreement duration.

•

The process for amendment and termination of the agreement.

•

A process for resolution of any conflict.

•

The type of issues of mutual concern covering everything from establishment of boundaries
through the process of annexation.

Establishment of an interlocal agreement includes a 19-step process, which has been included in
Appendix E. Currently, establishing a joint planning effort for a single issue takes 3 to 6 months and
multiple issues takes 6 to 18 months to establish.
8.5

POTENTIAL WASTEWATER SYSTEM IMPACTS

In order to understand potential impact of expanding the collection system south of the current UGA
boundary, the projected wastewater flows and impacts to the WWTP are presented.

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8.5.1

Southern Region Projected Wastewater Flow

Table 8-1 indicates the additional acreage that could be added to the City’s service along with additional
MMF for each of the proposed expansion areas.

Average wastewater flow was assumed to be 1,300 gpad with I/I flow of 500 gpad and a peak factor of 2.2.
Joint Planning Area

At build-out conditions, the potential additional MMF would be between 0.50 and 1.88 mgd depending
upon the final size and shape of the expansion area selected.
8.5.2

Future Treatment Plant Capacity

The addition of the southern service area to the City’s UGA impacts the available capacity at the City’s
treatment plant. Gray & Osborne, who is currently designing the WWTP expansion, reports that the
treatment plant is to be expanded to accommodate a MMF of 4.59 mgd for the year 2017.
The City of Sumner’s portion of the 2002 – 2003 expanded treatment plant’s MMF capacity is
approximately 53.3 percent (Sumner’s expansion cost), or 2.45 mgd of flow from the City. Parametrix has
projected that the build-out MMF for the existing UGA boundary will be approximately 2.5 mgd in the
year 2023. Therefore, the City of Sumner’s apportionment of the 2002 – 2003 expanded treatment plant
capacity will be expended on providing service to the existing UGA boundary.
Any expansion of the collection system service area into the southern region will require the City to
eventually construct additional treatment plant capacity.
8.5.3

Available Land for Treatment Plant Expansion

Land must be available for expansion of the treatment plant. The following section will examine available
land on or around the existing wastewater treatment plant. To estimate the area available for future
treatment plant expansion, the following assumptions have been made:
•

No land buffers due to river setback requirements.

•

No land buffers due to odor control measures.

•

Buildable condition of 100 percent of the available land.

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The existing wastewater treatment plant covers approximately 3.6 acres of the 8.8 acres the City owns
around the treatment plant (see Figure 8.2). The 2002 – 2003 proposed wastewater treatment plant
expansion should cover an additional 2 acres. Therefore, the City will have approximately 3.2 additional
acres available for any additional treatment plant expansion in the future.
In addition to City-owned land, the State owns approximately 2 acres of land that adjoins the City’s
treatment plant site and other private parties own the remaining bordering land.
Based upon the availability of additional City, State, and privately-held land, the City should not have any
problems with future expansion plans associated with serving the service area.
8.6

SUMMARY

It is recommended that the City of Sumner determine the desired size and shape of any future southern
service area before pursuing the interlocal agreement with Pierce County for a Joint Planning Area.
The City should also consider which of the following issues they wish to resolve with the County prior to
applying for the agreement:
•

Land-use patterns

•

Zoning designations

•

Development standards

•

Design standards

•

Environmental standards and policies

•

Level of service standards

•

Service provider (who will provide which service)

•

Growth tiers

•

Public lands

•

Essential public facilities

•

Capital facilities

•

Project review and approval for developments

•

Annexation and transition timeline

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Not all of these issues must be agreed upon prior to execution of the agreement with Pierce County. It is
recommended that the City enters into the interlocal agreement addressing issues of immediate concern,
and negotiate the remaining items in the future. Issues of immediate concern include:
•

Zoning designations

•

Growth tiers

•

Development standards

•

Design standards

•

Level of service

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9.
9.1

FINANCING PLAN

INTRODUCTION

The financing plan discusses the need to generate additional sewer revenues to implement the
improvements discussed within this report. Recommended collections system improvements include
additional system capacity and upgrades. The financing plan also considers improvements necessary to
expand the capacity at the City’s wastewater treatment plant as outlined in the Wastewater Treatment
Facility Final Comprehensive Facility Plan Amendment No. 1 as prepared by Gray & Osborne (G&O).
Both sewer and treatment improvements need revenues to be implemented, which will have an impact on
the sewer fees currently levied by the City. To have an understanding of the total impact to the City sewer
utility fees, sewer and treatment plant improvements must be considered together.
It is assumed that funding for capital improvements will be generated through sewer fees. Sewer fees
currently levied by the City of Sumner include:
•

A sewer utility rate that is charged on a monthly basis, and

•

A one time System Development Charge (SDC), which is levied at the time that sewer service is
provided.

9.1.1

Sewer Utility Rate

Prior to 1999, the City of Sumner’s sewer utility rate was based upon a fixed charge per equivalent
residential unit (ERU). This flat rate structure contained an annual adjustment for inflation based upon the
Engineering News Record (ENR) Rate Index. In 1998, the City of Sumner generated approximately
$1,230,000 (see Table 9-1) based upon a flat rate sewer fee of $23.45/ERU.

Table 9-1. City of Sumner Sewer Revenue
Year

Total Revenue Collected

Bonney Lake Charge

Sumner Sewer Revenue

1998

$1,533,000

$303,000

$1,230,000

1999

$1,505,000

$442,000

$1,063,000

In January 1999, the City of Sumner changed the flat rate billing structure to a combined fee structure.
The combined fee structure consisted of a base rate and usage (water consumption) fee. The following is a
summary of the 1999 fee structure:
•

Base Rate = $5.15/ERU

•

Usage Fee = $2.47/100 ft3 of water usage

The change in the rate structure reduced the City’s revenue stream from 1998 as shown in Table 9-1.

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In January 2000, the City increased the sewer fee structure to the following:
•

Base Rate = $5.31/ERU

•

Usage Fee = $2.95/100 ft3 of water usage

The 2000 change in the sewer utility rates has not been in effect long enough to determine the impacts on
the annual sewer revenues.
An estimate of potential 2000 revenues was conducted by comparing the 1999 utility rates with the 2000
utility rates based upon the average water consumption of a typical single-family home. The comparison
indicated that the City could have a revenue increase of approximately 16 percent resulting from the
changes in the 2000 utility rate. The total 2000 annual sewer revenue is estimated at approximately
$1,240,000, which is similar to the revenues generated by the City in 1998.
9.1.2

System Development Charge (SDC)

The City of Sumner charges each new customer a one time SDC at the time of connection to the sanitary
sewer system. The SDC allows the City to generate additional revenue to finance capital system
improvements. Currently, the City of Sumner’s SDC for connection to the collection system is $2,011 per
equivalent residential unit (ERU). Table 9-2 summarizes revenues generated over the last three years.

Table 9-2. System Development Charge Revenues
Year

Total SDC Revenue

Number of New ERUs

1997

$357,447.05

201.2

1998

$234,582.53

125.3

1999

$698,123.94

358.0

Rates for SDC change each year (October 1) due to inflation or institution of rate adjustments.

9.2

RECOMMENDED SYSTEM IMPROVEMENTS

The system improvements summarized in the following tables have been identified in two separate
engineering reports. The recommended collection system improvements were developed in Chapter 5 of
this report and the recommended treatment plant improvements are listed in the Wastewater Treatment
Facility Final Comprehensive Facility Plan Amendment No. 1 as prepared by Gray & Osborne.

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Sanitary Sewer Comprehensive Plan Amendment

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The recommended improvements have been separated into two categories, system capacity improvements
and system upgrades, as listed in Table 9-3.

In addition to the recommended improvements to the collection system, the City of Sumner is in the
process of expanding the wastewater treatment plant’s hydraulic capacity and improving the treatment
process to meet more stringent NPDES discharge standards. The preliminary estimated cost for the
treatment plant improvements is $16,609,384. The City of Sumner’s portion of the improvements is
53.3 percent, of $8,852,802. Table 9-4 separates the City of Sumner’s share of the treatment plant costs
into improvements needed to increase capacity and improvements needed to meet current treatment plant
discharge standards. The share of cost in each category was provided by the City of Sumner Public Works
Department.

Table 9-5 provides a summary of the total recommended improvement costs. The costs for collection and
treatment are separated into 1) capacity improvements, or 2) upgrades to the collection system and
treatment plant to meet new regulatory requirements.
Table 9-5. Total Recommended Improvement Cost
System Capacity Improvements

Recommended System Upgrades

Collection System Improvements

$5,754,600

$8,826,300

WWTP Improvements

$5,417,900

$3,434,900

$11,172,500

$12,261,200

TOTAL PROJECTED COST

9.3

EXISTING DEBT SERVICE

The City of Sumner currently is paying for existing debt service through sewer rates and other revenues.
Because this outstanding debt has an impact on the existing sewer utility rate, it has been included in this
report. The City of Sumner has three outstanding revenue bonds listed in Table 9-6 that are partially paid
by sewer utility rates. The 1998 and 1993 bonds are for purchase of property to provide the City of
Sumner the option of land applying treated effluent during the summer months to meet NPDES discharge
permit limits. Approximately half of the land purchased is currently being used for a golf course owned
by the City. The 1992 refunding bond was for sewer improvements throughout Sumner’s service area.
Table 9-6. Existing Debt Service
Annual Payment in Thousands(a) 1999 Dollars
Description

According to financial staff at the City, Sumner receives approximately $200,000 in revenues from the
golf course and an additional $40,000 in revenues for lease of the undeveloped portion of property.
9.4

FUNDING STRATEGIES

Two separate funding options were considered to generate capital to pay for the recommended
improvements.
•

Funding Option 1 Assumptions:
¾ Capacity improvements will be paid by revenues generated from SDC.
¾ Upgrades to the system will be paid through sewer utility rates.
Option 1 also assumes that the existing debt will continue to be paid for by revenues generated by
sewer rates, and revenues from the golf course and land lease.

•

Funding Option 2 Assumptions:
¾ Capacity improvements will be paid by revenues generated from SDC.
¾ Upgrades to the system will be paid through sewer utility rates.
Option 2 assumes that half of the existing annual debt payment will be paid for by revenues
generated by SDC and that the remainder of the debt will be paid for by revenues from the golf
course and land lease.

Funding Option No. 1
Funding Option No. 1 assumes that capacity improvements are paid by the System Development Charges
as shown in Table 9-7. The City’s SDCs would need to be increased approximately 15 percent from the
current rate of $2,011 to $2,318 as shown.
Table 9-7. Funding Option No. 1 – Projected SDC Charge (1999 Dollars)
Recommended Capacity Improvement

Projected SDC Charge

Treatment Plant

$5,417,900

$1,205(a)

Collection System

$5,754,600

$1,113(b)

TOTAL
(a)

(b)

$11,172,500

$2,318

Capacity improvements of $5,427,900 divided by 4,495 ERUs. The 4,495 ERUs represent projected additional ERUs in
a 20-year period.
Capacity improvements of $5,754,600 divided by 5,170 ERUs. Total ERUs calculated by adding projected residential
ERUs of 4,494 and commercial/industrial ERUs of 676 for the next 23-year period.

This analysis does not include any additional increase for inflation since the current rate structure contains
an annual inflationary adjustment.

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Sanitary Sewer Comprehensive Plan Amendment

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May 2000

All system upgrades are paid for by sewer utility rates as shown in Table 9-8. It is also assumed that the
existing debt payment that is partially paid for by rates would continue to be paid by rates. To implement
the improvements identified for both the collection system and the treatment plant, the City would need to
increase revenues by approximately 50 percent.

The recommended rate change would result in a monthly sewer charge for a typical single-family home of
approximately $35 to $38 per month.
Funding Option No. 2
Funding Option No. 2 assumes that capacity improvements are paid by the system development charges
as shown on Table 9-9. The SDCs will also pay for half of the City of Sumner’s current debt payment.
This funding option assumes that at least half the value of the land purchased for land application would
be considered applicable to addressing future plant capacity. The City’s SDCs would need to be increased
approximately 67 percent from the current rate of $2,011 to $3,362 as shown.
Table 9-9. Funding Option No. 2 – Projected SDC Charges
Recommended Capacity Improvement

Projected SDC Charge

Treatment Plant

$5,417,900

$1,205(a)

Collection System

$5,754,600

$1,113(b)

$235,000

$1,044(c)

50% of Current Annual Debt Payment
TOTAL:
(a)

(b)

(c)

$3,362

Capacity improvements of $5,427,900 divided by 4,495 ERUs. The 4,495 ERUs represent additional ERUs in a 20-year
period.
Capacity improvements of $5,754,600 divided by 5,170 ERUs. Total ERUs calculated by adding projected residential
ERUs of 4,494 and commercial/industrial ERUs of 676 for the next 23-year period.
Calculated by dividing recommended capacity improvement by 225 ERUs per year.

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This analysis does not include any additional increase for inflation since the current rate structure contains
an annual inflationary adjustment.
All system upgrades are paid for by sewer utility rates as shown in Table 9-10. Under this funding option,
sewer utility rates would no longer need to support the existing debt payments not covered by golf course
or lease revenues. To implement the improvements identified for both the collection system and the
treatment plant, the City would need to increase utility rates by approximately 33 percent, which would be
19 percent less than Funding Option No. 1.

Percent increase in sewer rates determined by dividing total annual cost by projected 2000 revenues of $1,240,000.
From City of Sumner/G&O estimates for recommended plant upgrades.
Based upon G&O report Table 7-10. Calculated by multiplying annual treatment plant debt payment of $393,000 by
recommended upgrades percentage of total treatment plant improvement cost (38.8%)
From G&O treatment plant report Table 7-6. G&O projected additional annual O&M of $192,950 multiplied by City of
Sumner’s portion of 53.3%.
Parametrix estimates for recommended collection system upgrades, Table 6-1.
Capital costs of $8,826,300 divided by planning period of 23 years.
Reduction of half of the annual debt service as determined in the SDC table.

The recommended rate change would result in a monthly sewer charge for typical single-family home of
approximately $31 to $33 per month.
9.5

ADDITIONAL FINANCIAL ANALYSIS

To finalize the financial element of the sanitary collection system and treatment plant, it is recommended
that the City of Sumner conduct a detailed financial analysis prior to implementing rate adjustments. A
detailed financial analysis will confirm or deny the impacts of the recommended system improvements on
the existing sewer rate fees.

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The financial strategies that the analysis should consider include:
•

A cash flow analysis that determines the effect on the recommended utility rate increase
including:
¾ Implementation of the recommended improvements to the wastewater treatment plant.
¾ Implementation of the recommended improvements to the collection system.

•

An analysis to determine if the current debt payment could be paid for by SDCs as listed in
Funding Option No. 2.

•

The effects of Initiative 695 upon any proposed rate increase.

A detailed financial analysis of the City of Sumner’s rate structure has not been included at this time for
the following reasons:
•

The estimated construction cost for the wastewater treatment plant will adjust throughout the
design stage. Construction cost estimates are more accurately determined in the financial analysis
if prepared close to the beginning of construction.

•

There has been sufficient time under the January 31, 2000, rate increase to assess the true
financial effects.

•

The City needs to determine if portions of the current debt payment can be supported by the
SDCs.

9.6

SUMMARY

It is recommended that the City Council and the Utility Department consider Funding Option No. 2 that
includes a combined SDC and sewer rate increase, along with payment of a portion of the current debt
through SDCs. The option is more equitable to both existing and future collection system customers for
the following reasons:
•

Growth pays for growth – The future sewer system customers would pay for the capacity
improvements necessary to provide them service.

•

Existing pays for existing – The customers who have been using the system would be responsible
to pay for the system upgrades that benefit all customers.

Sanitary Sewer Comprehensive Plan for Sumner

It is the intent of this document to analyze the City’s collection system and to identify system deficiencies for existing and future flow conditions. If any deficiencies are identified in the City’s collection system, improvement and cost recommendations will be developed.